Metallized plastic film material is used for a wide variety of packaging operations. The film is made by vapor depositing a layer of the metal, usually aluminum, on the polymeric substrate, and it has previously been suggested to mask portions of the polymer substrate to prevent metal vapor deposition thereon and thereby provide a transparent area or window through which product packaged in a package formed from the film may be viewed. The major problem with the provision of such windows is lack of color compatibility for colors which are printed both on the window area and the metallized area. Further, patterns more intricate other than simple windows have not been produced on metallized plastic film by this masking method.
It has previously been suggested in U.S. Pat. No. 4,242,378 to provide a pattern of see-through portions and opaque portions on a metallized plastic film by forming a pattern of a water-insoluble resin on the metal layers corresponding to the opaque portions and immersing the resulting film in an aqueous solution of a metal solubilizer to dissolve the exposed metal while leaving untouched the patterned portion to form the see-through portion in the dissolved metal areas. Although this process is capable of producing colored printing by using resin-based printing inks, the procedure is time consuming and incapable of rapid continuous operation.